Saving Soil and Yield

Long-Term Missouri Study Touts No-Till and Crop Rotation

Soybeans in a long-term tillage study at the University of Missouri yielded better in a no-till system over the course of 20-plus years. (DTN photo by Katie Micik)

COLUMBIA, Mo. (DTN) -- Missouri cropland was hemorrhaging nearly 7 tons of soil per acre each year when Bill Wiebold began his long-term tillage and crop rotation study in 1992.

More than two decades later, the state's erosion rates have ebbed, and Wiebold's studies have validated the no-till and rotation practices that helped that happen.

"We've made lots of progress, but we don't ever want to go back," the University of Missouri agronomist told attendees of the annual MU Crop Management Conference on Dec. 16.

Farmers shouldn't have to, he added. Data from his two-decade study shows that overall, no-till fields yield as well and sometimes better than tilled fields, even in the poorly draining clay pan soils of his central Missouri plots. Another long-term study on crop rotations showed yield advantages of nearly 14% and 10% in rotated corn and soybeans, respectively.

CRUNCHING THE NUMBERS

Wiebold's test plots have been home to some seriously pampered corn and soybeans. In an effort to remove all factors but tillage from his first study, the fields were planted on the same day, hand-weeded diligently all summer, and the corn fields received a whopping 280 pounds of ammonium around planting time.

The researchers used a chisel plow for primary tillage, and then either a disc or cultivator for secondary passes in the tilled plots. The crops were never irrigated, with the exception of the drought in 2012, when Wiebold doled out just enough water to keep them alive.

In the corn-soybean rotations, the no-till system did very well, Wiebold concluded. Soybean yields showed a 5.3% advantage in the no-till fields (50.1 bpa v. 47.6 bpa) and corn yields showed no significant difference between the tilled and no-till fields.

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Patience is key -- with both your soil and yourself, Wiebold added. "The first three years, no-till yielded less than till," he said. "It takes some time for those plots to equilibrate."

Regardless of the tillage practice, soybeans rotated with corn yielded around 9% better than continuous soybeans in the tillage trial.

In another study started in 2005 and devoted entirely to crop rotation, the differences were even starker. Soybeans rotated with corn out-yielded their continuous counterparts by nearly 10% and the rotated corn crops out-yielded continuous corn by nearly 14%.

BEYOND YIELD

Measuring the benefits of no-till systems and crop rotation outside of yield responses is tricky, but Wiebold and his graduate students have made a good start.

In the springs of 2013 and 2014, Wiebold's students cut small squares out of each trial plot after planting, measured the dried residue, and then put them back. The plots with no-till corn-soybean rotations were the clear winners and boasted a healthy average of 6,600 pounds of residue per acre. On the other end of the spectrum, the tilled plots with continuous soybeans averaged only 400 pounds of residue per acre.

When the researchers measured soil organic carbon in the top 2 inches of soil, the rotated no-till plots beat their tilled counterpart by two-tenths of a percentage point. That sounds small, but actually represents an added 6,700 pounds of soil organic matter, Wiebold noted.

Likewise, the top 2 inches of no-till plots showed a significant increase in the amount of active carbon, which serves as food for soil microbes.

Those microbes appear to be far busier in the no-till fields, as well. Researchers measured significantly more carbon dioxide emitting from the soil of the no-till plots. "That comes from the microbial activity, as it breaks down organic matter and from the roots, as they respire," Wiebold explained.

These measurements are "only dipping our toes into the pool of soil health," he told his audience.

Wiebold has also recently launched a long-term cover crop study. Half of the plots are planted with a cereal rye and tillage radish mixture, just after leaf drop in soybeans.

"Somebody who lives longer than me will be able to collect that data, and when you're here in 2030, they'll be able to show you the results," he said.

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Emily Unglesbee

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